1. Field of the Invention
The invention relates to a module circuit board including a plurality of I/O terminals disposed at an edge of the board, a plurality of soldering pads on its surface for mounting parts such as semiconductor devices, and a barrier formed on its surface to isolate the I/O terminals from solder.
2. Description of the Related Art
A module circuit board for mounting flat type package ICs using a Surface-Mounted Device includes a plurality of I/O terminals plated of gold or flash gold which is formed on its one edge, a plurality of soldering pads on its surface on which the ICs are mounted using a solder reflow process, and a solder resist film formed on the circuit board. In the solder reflow process, some problems occur. That is, during the performance of the solder reflow process, solder balls are formed from melted solder. The solder ball is moved on the resist film, which is disposed between the pads and the terminals. If the solder ball reached the terminal is adhered to the terminal, the circuit board will be defective. To avoid this problem, the following countermeasure has been taken.    (1) To avoid the formation of the solder ball, some conditions of the reflow process, including the temperature, are changed.    (2) To prevent the solder ball from reaching the terminal, the terminal is sealed with a tape before the reflow process.
In the measure (1), the frequency that the solder ball is formed can be decreased. However, it is difficult to eliminate the formation of the solder ball completely. In the measure (2), the cost performance is not effective because of sealing and removing the tape. Further, if the tape adhesive remains on the terminal, it becomes a problem when the board is connected to the other parts.